Oscillation generation



eb. 13, 1934. J, L, HNCH ET AL 1,947,003

OSCILLATION GENERATION Filed Dec. 3, 1930 3 Sheets-Sheet 1 WSH rllllmlr-l /Jn a 38 3 111- l? 2 INVENTORS J. L. FINCH BY 1w foNKLlN TTbRNEY Feb. 13, 1934. J NCH Er AL 1,947,003

osoILLATIoN GENERATION Filed Dec. 3, 1930 3 Sheets-Sheet 2 Jig. 5 60 INVENTORS J. L. FINCH J. C KUN rATTRNEY Feb. i3, 1934. 1 F|NH Er AL 1,947,003

OSC ILLATION GENERATION Filed Dec. 5, 1930 3 Sheets-Sheet 5 Iig. 5

f/ /OL 1 ff ff 122 ATToRNEY Patented Feb. 13, 1934 osoILLATIoN GENERATION James I. Finch, Patchogue, and ames W. Conlr lin, Rocky Point,v N. Y., afssgnors tovRadio C oxjporation of America, a corporation of Delaware Application December 3, l1930. Serial No. 499,642

23 claims. (ci. 256;-36)

This invention relates to oscillation generation and especially towards apparatus for the generation of relatively high frequency oscillations such as described in our copending application Serial Number 363,660, led May 16, 1929, wherein, in an electron discharge device oscillator, energy is returned aperiodically from an output circuit of the oscillator, to an input circuit thereof over a long transmission line a correct number of half wave lengths long for a desired frequency of oscillation. In this manner, by virtue of the fact that screen grid tubes and appropriate circuit shielding are used in order to prevent interelectrode and stray intercircuit feed back, regeneration takes place solely along the transmission line, the frequency for which the line is a whole number of half Wave lengths long being especially favored; whereas, energy of other frequencies are discriminated against and suppressed. As a consequent result of this structure, oscillations of very constant frequency are produced.

One of the objects of our present invention is to provide a pushpull oscillation generator or amplifier having long lines for coupling input and output circuits of the electron discharge devices forming the generator or amplifier, as the case may be, for controlling the frequency of oscillation thereof.

It is a further object of our present invention to use, in connection with a long line controlled pushpull oscillator or amplifier, means for the preventing of the effects of feed back, such as that through the interelectrode capacity of the tubes, giving rise to parasitic oscillations so that feed back occurs solely along the long lines associated with the electron discharge devices.

As described in our copending application interelectrode feed back may be prevented by the use of screen grid electron discharge devices combined with effective isolation or shielding of the circuits; but, it is a further object of the present invention to provide in combination with along line controlled oscillator, additional or other means for preventing the effects of interelectrode feed back. The latterV may take the form of a neutralizing scheme wherein either aninput or an output coil is split and connected to either an output or input electrode as the case may be, through neutralizing capacitors. The neutralizing system may, of course, be used with either single tube oscillators or amplifiers or in combination with oscillators or amplifiers of the pushpull type.

A further object of the present invention is to provide for the ready and simple adjustment in length of the long line or lines coupling input and output circuits of an electron discharge device or devices, and this we do by placing in the lines U-shaped conductive slides, preferably called ltrombone slides.

Heretofore, the frequency controlling lines were' directly connected through one or more block-ing condensers to input and output circuits of an electrondischar'ge' device. A further object of the present invention is to provide for the inductive coupling of the line to the circuits. The inductive coupling may be to Veither or both the input and output circuits, but we prefer to use inductive coupling of the line at its input end to Van output circuit and direct connection of the line at its output end to an input circuit of an electron discharge device or devices.

Another object ofthe present invention is to disclose a method for coupling the line to the devices such that for a desired frequency, potentialsfat the anode and control electrode of the device, appear substantially 180 degrees out of phase. This we do by uncoupling the line at its input end and by feeding to the line from, for example, a crystal oscillator, energy of a desired frequency. The output tapping point to the line is then Vmade substantially one-quarter wave length from the end of the line over'which portion of the line reiiection takes place. The correct quarter wave length spacing can be ascertained by the maximum reading of an ammeter in the output circuit of the electron discharge device oscillator under adjustment. When the quarter wave length point has been ascertained, the input end of the line can be coupled to the output circuit of the electron discharge device or devices, and the input tappingpoint is adjusted such that a maximum readingagain occurs in the ammeter in the output circuit of the electron discharge device or devices, as the case may-flic, at which time the portion of the line included between the tapping points will be a correct whole number of half wave lengths long at tliedesired, initially impressed, frequency. Rather than moving a tapping point along the line, a trombone slide, already referred to, may y be, and is preferably, inserted in the line and is adjusted to give correct line length.

As the line is simple in construction and can handle large amounts of power, higher power oscillations may be directly generated in the oscillator, modulated and radiated. However, in order to have the modulating energy handle a lesser amount of high frequency energy, it is a further object of the present invention to provide a system wherein modulating energy is applied to the screen grids of a pair of pushpull connected screen grid electrony discharge devices. The output of the screen grid devices isfed to a pushpull connected amplifier, Whose output circuit is coupled to the control electrodes of the screen grid tubes through long lines whereby both pairs of tubes act as a chain oscillator. The system offers the advantage that the modulator tubes, namely, the screen grid tubes reico ferred to, handle a much less amount of power, as a result of which, modulation can be accomplished much more easily. The output of the amplifier is then directly radiated or further amplified as desired, before further transmission.

Still a further object of the present invention is to provide a built-up line for use in connection with long line frequency apparatus of the character described such that velocity along the built-up line will be low, giving, in the case of shorter wave lengths, a great number of electrical wave lengths along its length, or allowing of the use of long line frequency control for longer wave lengths. The built-up line may be made of concentric conductors having a dielectric of high value therebetween such as pure water or sulphur, or, the long line may be made up of lumped inductors and capacitors, the inductors being properly shielded and uncoupled from each other.

In the accompanying drawings which are illustrative only of our present invention, and consequently not to be considered in any way limitative thereof,

Figure l illustrates a transmitter comprising an electron discharge device oscillator having long line frequency control means together with Capacity neutralization means for preventing the eifects of interelectrode feed back;

Figure 2 illustrates a system similar to Figure l wherein the split plate coil type of neutralization is utilized, and which system has means for inductively coupling the long line to a circuit of the electron discharge device oscillator;

Figure 3 illustrates a transmitting system having a pushpull type of oscillation generator having long line frequency control means, the long lines having U-shaped slides therein for varying their effective lengths;

Figure 4 is a system similar to that shown in Figure 3 wherein screen grids are used for preventing the effects of interlectrode feed back, the long lines for frequency control being in the form of coils, and coupled inductively to both input and output circuits of the oscillator devices;

Figure 5 illustrates a transmitting system wherein modulating energy is fed to the screen grids of a pair of pushpull connected screen grid electron discharge devices, feed back for the production of high frequency energy occurring from the output circuit of the pushpull amplifier to the control electrodes of the modulating devices; and,

Figures 6 to 9 inclusive, illustrate types of long line construction for use on longer wave lengths.

In Figure l, electron discharge device oscillator 2 is first capacity neutralized by the use of a split input coil 4 coupled at its lower end through a variable neutralizing capacitor 6 to its anode 8. A long line 10, a correct number of half wave lengths long, at a desired frequency, is then added coupling the tunable input and output circuits of electron discharge device 2 through blocking condenser 12 which oifers no appreciable impedance to currents of the desired frequency. By making the line 10 an odd number of half wave lengths long, and, by virtue of the aperiodic transfer of energy over line 10 caused by the provision of surge impedance` 14, either in the form of a tuned circuit or preferably in the forni of a resistance,

the control electrode 16 and anode 8 fluctuate in potential 180 degrees out of phase, which, of course, is the correct condition for oscillation generation. As disclosed more fully in our copending application referred to, oscillation generation will occurusolely at thefrequency for which the line 10 is the correct number of half wave lengths long, other frequencies being discriminated against.

The oscillations generated may be modulated by applying suitable modulation potentials to transformer 18 whose secondary is placed in the anode supply lead of electron discharge device 2. Output energy appearing in tunable output circuit 20 may be directly radiated, but preferably, is fed into a pushpull amplifier 22 and thence supplied through suitable blocking condensers 24 to an antenna 26 for radiation purposes.

The reason for the use of capacity neutralization is to prevent interelectrode feed back which would allow of the generation of parasitic oscillation frequencies not desired. If desired, of course, the neutralization may be made only partial such that there is some interelectrode feed back, in which case, due to the fact that the greater part of the feed back will occur over line l0 oscillation generation caused by the interelectrode feed back will be pulled into step with the predominant oscillation generation caused by feed back over the long line 10.

The frequency controlling line need not be coupled as shown in kFigure 1, but may be inductively coupled to the output circuit 20 of electron discharge device 2 by means of a coil 28 (see Figure 2). In this case, the input end of the line is grounded through a blocking condenser 30. A trombone slide or U-shaped slide 38 may i be placed in the line for the purpose of obtaining accurate and simple adjustment of the length thereof. The line, as indicated in our copending application, may be made in coil form properly shielded and insulated. For telegraphy, keying potentials from suitable sources 34, 36, may be applied through the action of a suitable keying device 32 through the line to the control electrode of tube 2. The applied potentials act to cause electron discharge device 2 either to block or to generate oscillations.

The power amplifier 22 shown in Figure 2, is as illustrated, of the screen grid type, the choice of amplifier, being in general arbitrary. As also illustrated in Figure 2, the power amplier 22 may be modulated, operation of key 40 acting to impress upon the control electrodes of the tubes forming the power amplifier, either a blocking potential 42 or a current passing potential 44. JL

The keyed energy may'then be inductively fed, as in Figure l, to a directive radiating antenna 26.

In Figure 3, we have illustrated an oscillator of the pushpull variety having long lines, coupling the input and output circuits of the electron discharge devices forming the oscillator, for frequency stabilization and control. Each of electron discharge devices `46, 48 are capacity neutralized by the action of condensers 56, 52 crossconnecting their anodes and control electrodes. ,i

After being fully neutralized or partially so in accordance with what has been said hereinbefore, long lines 54, 56 are added containing length varying trombone slides 58, 60 and coupling to the output and input circuits of the tubes through blocking condensers 62, 64. Aperiodic transfer of energy-is insured by the use of a suitable surge resistance 66.

As illustrated, the tuning condensers in the input and output circuits are each formed of two condensers mounted for unicontrol, the condensers in each circuit having their rotors and stators cross-connected, such that, during rotation of the condenser capacity to ground remains constant. The input and output circuits are tuned approximately to the desired frequency, exactfrequency control being maintained by the use of the'long lines 54, 56 which are, as already described, a correct number of half Wave lengths long-for a desired frequency of operation.

Modulation may be accomplished by variation in anode potential by the application of modulating potentials to the secondary of a transformer 66 in series with the anode polarizing lead 68. The resulting modulating energy may be taken from a secondary winding 70, fed to a transmission line 72, and then radiated over asuitable antenna'74. If desired before radiation, the modulated energy may be amplified in a suitable ampliiier of any desired construction.

The advantages ofthe pushpull arrangement shown in Figure 3 reside mainly in the fact that for most purposes the power output is suciently great to be directly radiated as well as the fact that the symmetrical arrangement of the system allows of simple and rigid construction, and tends to lessen parasitic oscillation generation.

In order to economize space, the lines are preferably made, as illustrated in Figure 4, coiled in form, the trombone slides 5S, 60 being placed in series with the coils. Moreover, the input and output ends of the line may be, if desired, inductively coupled to both the output and input circuits 76, 78 of electron discharge devices 47, 49 here of the screen grid type'. A surge impedance 66 in this case is connected to the midpoint of the primary of transformer 80. To prevent the effects of interelectrode feed back, screen grid tubes 47, 49 are used, the screen grids of which are grounded through suitable condensers 82, 84 for energy or" radio frequency. By the use of a suitable resistance 86 a suitable biasing potential may be applied to the screen grids, and, by virtue of the modulation transformer 88 applying modulating potentials to the screen grids, modulation of the generated oscillations will ensue. As indicated, the modulated output may be directly radiated over a suitable antenna 74.

As the end turns of the coils forming the lines do not link with as many turns as the center turns of the coils do, the impedance along the coil varies as a result of which it is, at times, difcult to obtain pure aperiodic transfer of energy along the lines. It is desirable, therefore, to make the output tapping points 90, 92 of the lines approximately one-quarter wave length away from the termination thereof. The quarter Wave length of the line will then have a standing wave set up thereon due to the reiiection from its electrically open end and will cause a maximum transfer of energy into the input circuit of the electron discharge devices.

To obtain the quarter wave length tapping point, the input taps 94, 96 to the lines are removed and the input end of the line connected to an oscillator of known frequency, for example, a crystal controlled oscillator operating at the desired frequency. Points 90, 92 are then adjusted until the ammeter reading of the ammeter 98 in the anode lead to the tubes 47, 49 gives a maximum reading. Then, in order to obtain correct phase adjustment of the input taps 94, 96 to the line, they are moved along the line until the ammeter again gives a maximum reading. The antenna during this procedure should be disconnected.

The last maximum ammeter reading, indicates that the portion of the line included between the tapping points 90, 92 and 96, 94 is the correct Whole number of half wave lengths for oscillation generation at the desired frequency. This adjustment may be made very accurately by rst getting a rough maximum ammeter reading by adjustment of taps 94, 96 after which al closer and finer adjustment may be made by manipulation of trombone slides 58, 60.

In Figure 5 asystem is ill'trated wherein the modulation energy does not have to cope with or deal with large amounts of oscillatory energy. Modulation energy is fed through a modulation transformer 100 and applied to the screen grids ofA electron discharge devices 102, 104. The screen grids are suitably grounded for high frequencyenergy by virtue of screen grid grounding condenser 82. Ihe output circuit 106 of the screen grid tubes is coupled to a pushpull amplier 108 as shown, whose output circuit is coupled through long lines 110, 112 to the control electrodes of electronV discharge devices 102, 104. The lines, to make them truly aperiodic, are terminated by a surge impedance 114 of correct value.

In the manner describedthe amount of energy that need be transferred over the long lines is relatively less for the reason that the energy so transferred is built up again by the amplifying action of the modulator tubes 102, 104 and then fed to the amplifier tubes forming the pushpull amplifier 106. Consequently, the amount of modulation energy necessary to produce the desired modulation is lessened, whereby. the modulation tubes need only be of very small size and rating relative to the size and rating of the tubes forming amplifier 108. The output of the amplier 108 may be radiated over a suitable radiating antenna 74 coupled, as shown, to the output circuit of pushpull amplifier 108.

If for any reason it is desired to have a Very long line relative to the working wave length, or if it is desired to use long lines for frequency controlling relatively long waves, the long line structures shown in Figures 6 to 9 may be utilized to good advantage. By virtue of their construction, velocity along the line is materially reduced, asV a result of which, a given length of line may be electrically very long.

In Figure 6 the line is shown as being made up of an inductor 116 of relatively high inductance shunted at various points along its length by condensers 118. The inductor 116 should, of course, be properly shielded by a shield 120. This line may replace any of the lines diagrammatically illustrated in Figures 1 to 5 by connecting the terminating taps of the line to the terminals 122 of the line shown in Figure 6.

The construction of the line shown in Figure 6,

may be varied as shown in Figures 8 and 9 Wherein in Figure 8 the inductor 116 is made up of a:

plurality of uncoupled, separately shielded inductors 124. In Figure 9, the inductors 124 are placed in both sides of the circuit replacing the single conductor 126 of Figures-6 and S, of relatively low inductance.

Another type of line having low electrical velocity along its length is shown in Figure 7 and it comprises a pair of concentric conductors or pipes 128, 130 between which is placed a dielectric 132 such as pure water, oil or sulphur. Sections of this line may be connected serially together and if desired, it, as well as any of the other lines described, may be temperature controlled or built of materials unaffected in physical length by ambient variations in temperature.

Having thus described our invention, what We claim is:

1. In electrical apparatus of the character described, the combination of 'a pair 'of electron discharge devices arranged in pushpull fashion and having input and output circuits, one of which circuits is tuned approximately to a desired operating frequency, and long line means comprising transmission lines, long relative to the operating Wave length for coupling the control electrode and anodes of the devices together for accurately stabilizing the frequency at Which the devices operate to the desired operating frequency.

2. In apparatus of the character described, the combination of a plurality of electron discharge devices having their cathodes connected together and having input and output circuits, said output circuit having inductance and capacity and being tuned approximately to a desired operating frequency, and long lines, long relative to the operating Wave length coupling the input and output circuits together for accurately controlling and stabilizing the frequency at which the devices operate.

3. In electrical apparatus of the character described, a pair of electron discharge devices each having a plurality of control electrodes and having their cathodes connected together, input and output circuits coupled to electrodes of said devices, one of said circuits being tuned to approximately a desired operating frequency, long lines, long relative to the operating Wave length coupling together input and output circuits thereof for accurately controlling the frequency at which said oscillation devices operate, and means for polarizing a control electrode of each of said electron discharge devices at a suitable relatively positive potential.

4. In electrical apparatus of the character described, a pair of electron discharge devices connected in pushpull fashion, a long line, long relative to the operating wave length coupling anode and control electrode circuits of one of said devices, an impedance terminating said line whereby at a predetermined frequency energy transfer over said line is substantially aperiodic, and another long line, long, relative to the desired operating Wave length coupling anode and control electrode circuits of the other of said devices and an impedance terminating said other line whereby energy transfer thereover is substantially aperodic.

5. In electrical apparatus of the character described, an electron discharge device, input and output circuits therefor, one of said circuits being tuned to approximately the desired frequency of operation, a long line, long relative to the operating vvave length coupling said input and output circuits, for accurately controlling the frequency of oscillation at which said device operates, and means for neutralizing interelectrode feed back of said device.

5. In apparatus of the character described, the combination of a pair of electron discharge devices having their cathodes connected together, input and output circuits connected to electrodes of said electron discharge devices, one of said circuits being tuned to approximately a desired frequency of operation, long lines, long relative to the operating wave length coupling said input and output circuits of said devices together, for controlling the frequency at which said devices operate, and means for preventing the effects of interelectrode andrstray circuit feed back of the devices.

'7. In combination, an electron discharge device,

input and output circuits connected to electrodes of said device, one of said circuits being resonant to approximately the desired frequency of operation, a long line, long relative to the operating Wave length coupling input and output circuits thereof together for controlling the frequency at which said device operates, and an adjustable U-shaped slide Within the line for varying the length thereof.

8. In combination, an electron discharge device, input and output circuits coupled to electrodes of said device, one of said circuits being resonant to approximately a desired frequency of operation, a long line, long relative to the operating wave length coupling input and output circuits thereof together, for accurately controlling the frequency at which said device operates, an adjustable U-shaped slide Within the line for varying the length thereof, and means for neutralizing interelectrode feed back of said device.

9. In electrical apparatus of the character described, a pair of electron discharge devices, input and output circuits connected to electrodes of said devices, one of said circuits being resonant to approximately a desired operating frequency, the cathodes of said devices being connected together, long lines coupling the input and output circuits of the devices together, said lines being long relative to a desired operating wavelength and acting to accurately control the frequency at which it is desired that said devices should operate, and, U-shaped slides in each of said lines for varying the effective lengths thereof.

10. In electrical apparatus of the character described, a pair of electron discharge devices, input and output circuits connected to electrodes of said devices, one of said circuits being tuned to approximately a desired frequency of operation, said devices having their cathodes connectedtogether, long transmission lines coupling together the input and output circuits of said devices, said lines being long relative to a. desired operating wavelength and acting to accurately control the frequency at which said devices operate, U-

shaped slides in each of said lines for varying the L effective lengths thereof, and means for preventing the effects of interelectrode and stray intercircuit feedback of said devices.

l1. In electrical apparatus of the character described, a pair of screen grid electron discharge devices having their cathodes connected together, means for applying modulating potentials to the screen grids thereof, a pair of electron discharge devices connected together to act as a pushpull amplifier coupled to said screen grid electron dis- V charge devices, and longl lines, long relative to the operating Wave length coupling the output circuit of said pushpull amplifier, to the input circuit of said screen grid electron discharge devices, for controlling the frequency at which the system operates.

l2. In an oscillator comprising an electron discharge device and a long line, long relative to the operating wave length for controlling the frequency of oscillation thereof, the long line coupling input and output circuits of said oscillator, the method of coupling the line to the oscillator Which'includes disconnecting the line from the output circuit and feeding energy, to

the uncoupled input end of the line, of a desired j frequency, adjusting the output connection of the line until maximum current flovvs'through the electron discharge device, and then coupling the outputcircuit of the device to the input end of the line until maximum current again ilows through the device.

13. In combination, an electron discharge device oscillator having an input circuit connected to its input electrodes and an output circuit connected to its output electrodes, one of said circuits being tuned to approximately a desired frequency of operation, and a long transmission line, long, relative to a desired operating wavelength and acting to accurately control the frequency of operation of said electron discharge device oscillator, said long line coupling said input and output circuits together, said line being inductively coupled at one of its ends to one of said circuits.

14. In combination, in electrical apparatus of the character described, an electron discharge device oscillator, an input circuit connected to input electrodes of said device an output circuit connected to output electrodes of said device, one of said circuits being tuned to approximately a desired frequency of operation and each of said circuits including an inductor, and, a long transmission line coupling said circuits together, said long transmission line acting to accurately control the frequency of operation at the desired frequency, said line being inductively coupled at its input end to the inductor included in the output circuit of said electron discharge device oscillator.

15. Apparatus as claimed in claim 13 in conibination with means for preventing the effects of interelectrode and stray intercircuit feedback of said electron discharge device.

16. In combination, a pair of electron discharge devices having their cathodes connected together, an input circuit connected to input electrodes of said electron discharge device oscillator, an output circuit connected between output electrodes of said electron discharge device oscillator, one of said circuits being tuned to approximately a desired frequency of operation, and, a plurality of long transmission lines each of which is long relative to a desired operating wavelength coupling together said input and output circuits for accurately controlling the frequency cf operation of said devices at a desired operating frequency, said lines being inductively coupled to one of said circuits.

17. Apparatus as claimed in the preceding claim in combination with means for preventing the effects of interelectrode and stray circuit feedback of said devices.

18. In electrical apparatus of the character described, the combination of a pair of electron discharge devices arranged in pushpull fashion and long line means comprising transmission lines, long relative to the operating wave length for coupling the control electrodes and anodes of the devices together for stabilizing the frequency at which the devices operate, and, means for terminating said lines whereby waves of the operating frequencies travel substantially unidirectionally thereover.

19. In apparatus of the character described, the combination of a plurality of electron discharge devices having their cathodes connected together and having input and output circuits, long lines, long relative to the operating wave length coupling the input and output circuits together for controlling and stabilizing the frequency at which the devices operate, and, means for terminating said lines whereby waves of the operating frequencies travel substantially unidirectionally thereover.

20. In electrical apparatus of the character described, an electron discharge device, a long line, long relative to the operating wave length coupling input and output circuits thereof, for controlling the frequency of oscillation at which said device operates, means for neutralizing interelectrode feed back of said device, and, an impedance for terminating said line whereby waves of the desired operating frequency travel substantially unidirectionally thereover.

21. In electrical apparatus of the character described, a pair of electron discharge devices having their cathodes connected together, long lines, long relative to the operating wave length coupling input and output circuits of the devices together for controlling the frequency at which said devices operate, U-shaped slides in each of said lines for varying the effective lengths thereof, means for preventing the effects of interelectrode and stray intercircuit feed back of said devices, and, an impedance equal in value to the surge impedance of said lines for terminating said lines whereby waves of the desired operating frequency travel substantially unidirectionally thereover.

22. In electrical apparatus, an electron discharge device having within an hermetically sealed container an electron emitting cathode and a plurality of cold electrodes, circuits interconnecting said cold electrodes and cathode, one of said circuits 1ceing resonant to approximately the desired frequency of operation, one of the circuits comprising a divided reactor, an intermediate point of which is connected to said cathode, another point on said reactor being connected to one of said cold electrodes, and another point on said reactor on the opposite side of said intermediate pointbeing connected through a condenser to another cold electrode of said device, and, a transmission line long relative to a desired operating wave length and having substantially uniformly distributed inductance and capacity connected between said cold electrodes whereby said long transmission line accurately fixes the frequency of operation of said device at a desired operating frequency.

23. A system for transmitting amplitude modulated waves of constant frequency comprising a pair of pushpull connected electron discharge devices each having a cathode a grid a screen grid and an anode, means for applying moduiating potentials cophasally to said screen grids with respect to said cathodes, a parallel tuned circuit tuned to approximately a desired frequency of operation connected between said grids, a high frequency circuit connected between said anodes, a pair of pushpull connected vacuum tubes each having plate, control grid and cathode electrodes, a high frequency circuit connected between said control grid electrodes and coupled to said high frequency circuit connected between said anodes, a high frequency circuit tuned to approximately a desired frequency of operation connected between the plates of said vacuum tubes, a pair of transmission lines long relative to a desired operating wavelength coupling together said last mentioned high frequency circuit and the tuned circuit connected between the grids of said electron discharge devices, said lines acting to accurately stabilize the frequency of operation of said system at a desired frequency of operation, and a utilization circuit coupled to the output circuit connected between the plates of said vacuum tubes.

JAMES L. FINCH. JAMES W. CONKLIN. 

